Programmable oscillators of the type requiring digital inputs for providing frequency outputs such as, for example, delay line oscillators, are usually of the free-running type, with no capability for continuous locking to an external clock source. On the other hand, programmable oscillators having such a capability require an analog voltage input for frequency control.
The presently disclosed invention has the capability of providing continuous frequency control for digitally programmable oscillators through an arrangement including an accurate frequency reference, registers, a counter and a comparator. The arrangement is configured as an integral feedback path from the output of the digitally programmable oscillator to its input for providing the aforenoted frequency control via a counter-locked-loop.